A method for searching for similar images using an image local feature amount (local feature amount) has been proposed. In this method, first, a feature point (local feature point) is extracted from the image. As a document disclosing this technique, C. Harris and M. J. Stephens, “A combined corner and edge detector,” In Alvey Vision Conference, pages 147-152, 1988. is given.
Further, a technique for calculating a feature amount (local feature amount) corresponding to the local feature point based on the local feature point and its peripheral image information is known. A document disclosing the technique, David G. Lowe, “Distinctive Image Features from Scale-Invariant Keypoints,” International Journal of Computer Vision, 60, 2 (2004), pp. 91-110 is given. The image search is performed by matching local feature amounts.
Further, Japanese Patent Laid-Open No. 2011-43969 discloses an image feature point extraction method to obtain plural image data by fluctuating the image and narrowing down to stabled feature points to extract a feature point from image data.